A new member in the Department of Mechanical and Aerospace Engineering is an expert in finding out what it takes to make materials fail. One way to do that is to shoot them out of a gun.

Well, not a gun exactly, but a CSULB student-built high-strain impactor that uses compressed gas to accelerate projectiles to high speeds at Whisler’s new dynamic impact research and engineering lab. Sharing space nearby will be another student-made project, the low-strain impactor powered by less exotic means—simple gravity. “There will be no explosions,” Whisler cautions. “After all, you can’t see anything in a fireball anyways, just a lot of dust and debris. None of this is inherently dangerous.”

The low-strain impactor resembles a small swing and operates via gravity in a manner similar to cartoon character Wile E. Coyote holding a large mallet.

“At seven meters per second, the sample experiences up to 100 Joules of energy during impact. Its effect is a dynamic loading of the material,” Whisler said. “When things go faster, you typically get a different phenomenon in the material response compared to slower loading speeds.”

The high-strain impactor is where the fun begins for Whisler. Projectiles are used to load materials like carbon fiber panels to failure. “The barrel is between 15 and 20 feet long. The longer the barrel and the higher the pressure, the faster the projectile travels—speeds of up to 200 m/s are possible. On the opposite side of the specimen is a Hopkinson transmission bar that is equipped with sensors for measuring the force wave transmitted through the specimen,” he said. Since the entire impact zone is fully enclosed, viewing is done by high-speed camera capturing 100,000 frames per second.

His goal for his UC San Diego doctoral dissertation was to simulate an improvised explosive devise (IED) explosion on the underside of vehicles.

“I was asked to design an experiment to replicate blast-like conditions without the requisite fireball and dust clouds,” he said. “My solution was to design a 60 kg projectile with tiled blocks, each of which could move and rotate independently to replicate the spherical-like pressure wave of an IED explosion positioned just 12 inches away from the vehicle.”

Whisler received all three degrees in structural engineering from UC San Diego including his B.S. in 2007, his M.S. in 2009 and his doctorate in 2014.

The U.S. Navy wanted a 30 percent improvement in the performance of its materials. Whisler and his team visited the Oregon Ballistics Laboratory to personally witness the force of an explosive blast test.

“It’s weird,” he recalled. “The first time you are in an explosion, your whole body feels like it is being compressed instantly. It is as if you were suddenly dropped deep underwater for a split-second then it is gone.”

Their experiment concluded that the materials the military wanted to put on the bottom of their vehicles actually performed better than steel.

“They were thicker but lighter. But the most important thing was discovering we could test these materials without using explosives,” he said. “With the methodology we developed, the simulated blast pressure wave was dead-on accurate every time and provided a lot more data without breaking sensors.” This research could reduce the amount of time required for armor development to better assist military troops.

It can take weeks to plan a test that takes seconds or less to perform. It took Whisler 18 months of planning to execute his Ph.D. experiment, a matter of hours to do several tests, then several weeks analyzing the data.

“It is important, especially with the bigger projects, to perform all the high-speed testing at once,” he said. “That way, you minimize your costs. We had back-ups for everything including the high-speed cameras. For the bigger tests, you only have one shot so it’s good to have spares. If anything goes wrong that day, you fix it that day or you have to call the whole test off.”

Major benefactors of Whisler’s failure tests are those living in the paths of natural disasters.

“Look at the special needs of structures like hospitals,” he said. “They cannot have ANY down time. That is especially the case in a natural disaster. If your community is facing hurricanes or tornadoes, you want your hospitals, fire and police departments to be up and running. We have made progress in impact mitigation but still have a long way to go in designing structures to resist these natural disasters and even further for manmade disasters.”

PHOTO BY JOE PHILIPSON

Daniel Whisler

Students approach the chance to work in Whisler’s lab with enthusiasm. “It’s hard to keep them out of the door,” he said. “The research is 90 percent planning, nine percent evaluation and one percent testing. Even if the project is a paperweight, students here love to see the process from design to fabrication to final result. The thing about my research is that the paperweight is actually a projectile that goes fast and creates really precise impact loads. Those are the students I want the most—the ones who are eager to learn and have a mindset towards testing.”